Mark Martell had heard of birds flying into man-made structures, such as skyscrapers, wireless communication towers and wind turbines — often with fatal results.

But bridges?

That was a new one, even for Martell, the director of bird conservation for Audubon Minnesota.

“It might just be something about the height of the bridge, but I don’t know,” Martell said after hearing reports that migratory birds were flying into the new Hwy. 61 Hastings bridge or becoming entangled in the cables holding up the $130 million span that connects the historic river town to Washington County.

While environmentalists and bird experts have spent years studying how buildings in urban areas came to be such prolific bird killers, little such research has been done on bridges, Martell said.

In an effort to learn more, however, state transportation officials plan to hire an environmental firm to study the issue and possibly, come up with solutions for limiting bird kill.

“The bottom line is we just don’t know very much about it, so this (study) is something that interests us and many others,” Martell said.

The issue is particularly important for the tied-arch Hastings bridge, which spans the avian expressway that is the Mississippi River.

More than 300 species of birds — “millions, if not billions” — from hummingbirds and warblers to yellow-bellied sapsuckers, fly along the river to and from their wintering grounds in Central and South America, said the National Park Service’s Paul Labovitz, who serves as superintendent of the Mississippi River National River and Recreation Area.

“I watched a flight of pelicans one summer day flying over that took 15 minutes to pass over me,” Labovitz said. “So the numbers are staggering.”

At the prodding of the Park Service, the Minnesota Department of Transportation plans to undertake an environmental study this year to determine the bridge’s impact on birds.

“It’s a conversation that’s been going for actually a couple of years, but we’re getting to the point to where we’re actually trying to frame what the study’s going to be,” said Labovitz.

A MnDOT spokeswoman did not return calls for comment.

The study, which could cost up to $100,000, will address such issues as whether the bridge lights confuse night-migrating birds, who navigate by using the moon and stars, causing them to crash or become entangled in the cables.

Labovitz said he hopes the study will get architects to start thinking about bird-friendly design.

“We didn’t have the in­for­ma­tion to in­form this par­tic­u­lar bridge de­sign,” he said,” but we were hop­ing that this in­for­ma­tion would in­form fu­ture pro­jects.”

Next to feral cats and loss of habitat due to human development, ornithologists say buildings are the most prolific bird killers.

The U.S. Fish and Wild­life Service estimates at least 97 million and as many as 976 million birds are killed annually in the United States when they crash into buildings. But Labovitz says that number doesn’t take into account the millions more who slam into TV towers, wind turbines and bridges.

“You have to won­der in 2014 why we don’t know more about this top­ic,” Labovitz said.